The present invention relates to two stroke engines, and more particularly to two-stroke engines having scavenging or transfer passages with fuel injection.
Conventional two-stroke engines suffer from high hydrocarbon emissions and poor fuel efficiency because they use a fresh fuel-air mixture to scavenge the combustion chamber. It is known in the prior art to reduce the system-caused scavenging losses in two-stroke engines by advancing fuel-free scavenging air ahead of a fuel-air mixture. This reduces the fuel that is lost due to short circuiting fresh fuel-air mixture in the combustion chamber with the exhaust port.
Scavenging two stroke engines with stratified air-heads have been developed to address this problem. One example of such an engine is described in U.S. Patent Application No. 2004/0040522, filed May 28, 2003, and entitled Two Stroke Engine With Rotatably Modulated Gas Passage. In this design, the stratified air-head two-stroke engine inducts scavenging air from the top of transfer passages through reed valves or piston porting. However, this design also requires a special carburetor requiring two valves, one for air and the other for the air-fuel mixture.
For the foregoing reasons, there is a need for a two-stroke engine that eliminates the need for a custom designed carburetor and provides for self-regulating fuel-metering with improved engine performance.